A 28-year-old woman presents with gradually worsening exertional dyspnea and fatigue for the past six months. She now gets breathless after climbing a single flight of stairs. She has no significant past medical history and has always considered herself healthy, although she notes she could never “keep up” with peers in sports during childhood. She denies chest pain, palpitations, or syncopal episodes. She is not on any medications and has no known allergies. Family history is non-contributory for congenital heart disease. She does not smoke or use illicit drugs.